The present invention relates to the field of rolling-bearing rollers and, in particular, rolling-bearing belt-tensioning rollers, for example rollers used in the engines of motor vehicles in order to ensure adequate tensioning of a drive belt for an accessory of the engine, such as the water pump, the alternator, etc.
In a manner known per se, such rollers comprise a pulley or a rim mounted on the turning outer ring of a rolling bearing. The pulley is intended to come to bear radially against a belt. The nonturning inner ring of the rolling bearing is mounted on a support which makes it possible, by means of an appropriate system, radially to displace the rolling bearing and the pulley with regard to the belt and in this way to adjust the tension of the belt. The nonturning inner ring of the rolling bearing is fixed on the roller support by means of a screw. It is possible to use this screw to fix a leaktight end plate onto the device, providing supplementary protection of the rolling bearing against the ingress of undesirable pollutants originating from the outside.
Such devices are described in the documents DE-A-42 42 293 and DE-U 297 20 776.
Although such systems function correctly, they nevertheless have certain drawbacks.
The rolling-bearing roller, the fixing screw and the leaktight end plate consist of three distinct pieces which in the majority of cases cannot be preassembled, manipulated and transported without the risk of dismantling.
Moreover, when the rolling bearing is fixed onto its support, using the pinching of the end plate between the screw head and the face of the rolling bearing, it is difficult, for reasons of mechanical strength, to use nonmetallic end plates, which has a detrimental effect on the cost and weight.
In the case of document DE-U 297 20 776, the sheet-metal leaktight end plate is slipped into the bore of the inner ring of the rolling bearing, which requires a degree of precision in the manufacturing tolerances of the end plate at the location of the sleeving cylindrical bearing surface, resulting in an increase in manufacturing costs.
Tight steel/steel sleeving inevitably gives rise to geometrical variations in the inner ring of the rolling bearing, which are reflected in internal reductions in play which may be relatively difficult to control.
The invention proposes to solve all these problems.
The subject of the invention is an economical fixing device incorporating a leaktight means which does not risk becoming dismantled before final fixing and which does not affect the geometry of the inner ring of the rolling bearing.
According to the invention, the fixing device is intended for a roller of the type comprising a pulley mounted on a rolling-bearing device comprising a row of rolling elements arranged between a ball race provided on an outer ring integral with the pulley and a ball race provided on an inner ring. Said device comprises a screw comprising a cylindrical rod and, at one end of the cylindrical rod, a head provided with rotary-drive means. The device comprises a sleeve integral with the screw, said sleeve comprising means for fixing on the inner ring of the rolling bearing and leaktight means interacting with a turning part of the roller. The radial face of the screw head located on the cylindrical-rod side is provided with at least one passage allowing continuity of material between the fixing means and the leaktight means.
Advantageously, the sleeve is produced from synthetic material overmolded onto the screw.
In one embodiment of the invention, the screw comprises means for anchoring the sleeve.
Advantageously, the sleeve comprises an annular portion surrounding the cylindrical part of the screw over a part of its length.
In one embodiment of the invention, the annular portion of the sleeve is provided with an outer cylindrical surface capable of gripping in the bore of the nonturning ring of the rolling bearing. Said outer cylindrical surface may be provided with axial grooves.
Advantageously, the sleeve comprises a substantially radial portion, the inner edge of which is in contact with the screw head and the outer edge of which interacts with the turning part of the roller in order to form a seal, the inner edge of said substantially radial portion being cut into radii arranged in the corresponding grooves of the screw head. Said screw head may be capable of coming into contact with the inner ring of the rolling bearing.
In one embodiment of the invention, the screw comes into contact with the face of the rolling bearing via coplanar support surfaces which between them define radial grooves filled with plastics material in order to form radii, the thickness of the radii in the axial direction being equal to or less than the axial depth of said grooves.
In one embodiment of the invention, the sleeve is extended, axially away from the screw head, by radially elastic tongues equipped with hooks at their end, the hooks being capable of interacting with the radial face of the inner ring opposite the face in contact with the screw head.
A further subject of the invention is a fixing screw intended for a roller of the type comprising a pulley mounted on a rolling-bearing device comprising a row of rolling elements arranged between a ball race provided on an outer ring integral with the pulley and an inner ball race provided on an inner ring. The screw comprises a cylindrical part in the form of a rod which is at least partly threaded and, at one end of the cylindrical part, a head provided with rotary-drive means and a substantially radial support face arranged on the cylindrical-part side. The substantially radial support face of the head comprises at least one surface capable of coming into contact with a lateral face of the inner ring and at least one radial groove extending between the cylindrical part and the periphery of the contact surface.
In one embodiment, the screw comprises a plurality of axial protuberances facing the free end of the cylindrical part, said protuberances having a radial support surface, the axial protuberances being unconnected in such a manner that radial grooves are formed between them.
A further subject of the invention is a rolling-bearing roller comprising a fixing device.
Thus, the screw has the form of a partially or totally threaded cylindrical rod and of a head which is, for example, hexagonal, the radial face of the head located on the rod side being provided with axial protuberances which are separated from one another in the circumferential direction by spaces, the axial protuberances having radial surfaces which are intended to enter into contact with a lateral face of the inner ring of the rolling bearing and the spaces forming passages allowing continuity of material between the sealing part of the sleeve extending radially beyond the screw head towards the outside and the annular part of the sleeve located in the bore of the inner ring. Said radial surfaces of the axial protuberances allow direct contact with the inner ring. The sleeve may be formed by overmolding of plastics material and is secured with the screw in the axial direction owing to the thread of the screw or, optionally, of suitable reliefs formed on its rod and in rotation via the spaces and the axial protuberances mentioned above. The screw and its plastics sleeve thus form a particularly lightweight assembly which cannot come apart and is economical to produce. The tightening of the screw on the inner ring does not affect the sleeve, which has the same shape before and after tightening.